Method of and apparatus for liquefying gases



- Nov. 4, 1930. L. B. STRONG METHOD OF lAND APPARATUS FOR LIQUEFYING GASES Filed March 27, 19:50 2 sheets-sheet 1 INVENTOR. Lean 5.5570125,

ATTORNEY.

Nov. 4, 1930. L. B. STRONG 1,780,250

METHOD OF AND APPARATUS FOR LIQUEFYING GASES Filed March 2'7, 1930 2 sheets-sheet 2 II'II'IIIIIIIIJ INVENTOR.

Leaiz 5. Strong,

M /V44 I A TTORNE Y.

Patented Nov. 4, 1930 UNITED STATES PATENT oF lc LEON B. STRONG, 01 WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOB OF I PER CENT TO FRANK G. CAMPBELL METHOD OF AND APPARATUS FOR LIQUEFYING GASES Application filed Iarch 27, 1980. Serial in. 439,435.

This invention relates to a new process for the liquefaction of air and other gases, having an extremely low condensing temperature, and contemplates a near approach to 5 the minimum theoretical work necessary to agccomplish the liquefaction of such gases.

A further object of the invention is to eliminatecounter-current piping,,except in conjunction with the heat exchange in the work- 1o ing mediumfforvremoving the latent heat of the condensing vapor-,which medium is.con tained in a closed circuit being compressed at a convenient or easily attained temperature, cooled in the psual way and passed counter-current to the same medium in the expanded state. By virtue of this I am able to obviate the formation of frost, constituting one of the highly. objectionable features of known processes, on the inside surface of 2c the piping.

The invention also contemplates the performance of external work by the superheat of-" the gas to be liquefied, thereby increasing theefliciency-of the process, as a whole, and

more particularly increasingthe efliciency of the unit employed for the conversionqof the superheat of the gas into mechanical work. I am aware of the fact that this feature l alone is not new in the art,'but am, at present, unaware thatthe prior artoanticipates the removal either of' the superheat or the heat of vaporization, in this manner, without first cooling thetompressed gas to be liquefied counter-current with the expanded gas. This lowers the eificiency of the engine or turbine by'which the superheat of the gas is being converted into useful work by a well lmown' thermo dynamic la-w.v

Another very useful application of the in- 4 vention-resides in the separation of helium from natural 'gas, the heavy'hydrocarbons being disposed of inthe manner hereinafter described for the water'vapor content of air,

leaving chiefly nitrogen and methane" to be liquefiedin the manner in whichnitrogen and oxygen are liquefied, ashereinafter described, the helium being left as uncondensed residue. 4

' It may be ob ected'that this invention con- 60 templates primarilythe cheap quantity liquef faction of gases and'that the separation of helium:=is more a problem of distillation or rectification not dependent upon cheap quantity production of liquefied gas for its success. In this connection it should be borne 55 in mind that methane CH,, the chief constituent of helium bearing natural gases, due to its relatively large proportion of hydrogen furnishes a great deal more heat units per unit of weight than does gasoline. Therefore, liquid methane could be carried in suitable thermos tanks upon aeroplanes and furnish a much lighter fuel for air craft than any now economically possible. This fee-- ture I regard as much more important than liquid state, thereby greatly reducing both "the gross weight handled and the bulk of the delivery containers. The invention contemplates the removal of the total heat of the vapor in two distinct steps: First, the removal of the superheat of the vapor by adiabatic expansion, preferably, against a turbine, the expansion taking place so suddenly that a close approach to a pure adiabatic expansion occurs. Second, the removal of the latent heat condensation by ex- 4 panding in a plurality of stages a gas having a critical [temperature considerably lower I 1 than the condensing temperature of the vapor, preferably, against moving surfaces, to obsion, and returning the expanded gas to the compressor countercurrent, with the compressed gas supplying the engine.

' One form of apparatus which I may'em-.

'ploy in carrying out thenprocess above de- 95-' scribed is illustrated in the accompanying tain a closer approach to isothermal expan- V Fig. 3 is an oblique sectional view upon line 3-3 of Fig. 1,

view through parts in all the figures of the drawings.

I wilLdescribe the application of the a paratus in its relation to the liquefaction air. Its applicability in the other relations hereinbefore described will then be readily apparent to those'skilled in the art.

In the drawing, 5 designates an air compressor of any suitable orm, here conventionally shown as an ordinary piston air com pressor. The air compressed by the compressor is conducted by a pipe 6, to a turbine 7, the pipe passing through'a suitable water cooler, at 8. The gases are delivered to the turbine 7 through the nozzle 9 (see Fig. 3). It will be observed that the pipe 6 is restricted, as indicated at 10, at a point outside of the turbine. By virtue of this arrangement I am able to prevent the objectionable frosting which so frequently occurs in other li uefaction apparatus, at present employed. his isdue to the factlthatthe restricted portion of the pipe 10 is located at such a: point that it will always be at a higher tem erature than the temperature of the expan ing gases, and, consequently, the frost crystals will not adhere theretofi urthermore, this nozzle is insulated against heat losses by elements 18 and 19, hereinafter described. The impingement of the gases from thenozzle 9 upon the blades 11 of the moving rotor 12,'that iscarried by shaft 13, prevents the reversion of the energy of the' gases into heat. With expansion taking one hand, an

place suddenly a condition of super saturation of the water vapor content of the [bine 7 maybe widely varied. One type of air would occur, so that the frost crystals would not' form until after impingement of the 'et on the rotor blades, and then would not a here to the containing walls, being .formed in the air and carried along with it.

The motion of the shaft 13 may be utilized in the performance of .any useful work, as, for example, 5, or otherwise. The construction of the turconstrution is illustrated in Fig. 2, where 12 designates the rotor on shaft 13, said rotor being provided with the blades 11, and being received within the space between the two casing sections 16 and 17. A jacket 18 is formed about these sections in which a vacuum is maintained, and, in addition, these jackets may be more or less filled with sheets of metal foil, indicated at 19. These metal foilsh'eets serve to resist the passage of heat by radiation, and the vacuum serves to prevent the passage of heat by either conduction orjcotivection. 'However, suitably insulating thc yi tious parts ofv apparatus of this charin the driving of the compressor acter against heat losses is manifestly within the skill of the refrigerating engineer, and I contemplate insulating the apparatus against such heat losses to whatever extent ,7

spect to the turbine of Fig. 2. Located with in the casing 22 is a group of any desired number of turbines 23, the rotors of which are mounted upon the common shaft 24. The

shaft may be carried to the exterior of the condenser and used to do any useful .work

through the medium of the pulley, indicated at 25, or otherwise. The casing of each turbine is connected througha suitable ipe coil 26, with the casing of the next succeeding turbine, and the casing of the mechanically driven compressor 27, whichis substantially the same as the comp essor 5, is used to compress an independent gas medium such as hydrogen, having a critical temperature lower than the condensing temperature of the gas sought to be liquefied, and delivers the same throu h a run of pipe 28, to the casing of the first turbine of the group, in the condenser 22. The expanded refrigerating medium from the last stage or the last turbine is conducted through a pipe 29, and, preferably, counter-current to-the flow of gas in pipe 28, back to the hydrogen compressor 27, where it is re-compressed and the cycle repeated. A breather hole 20' may be left in the pi e 20 to compensate for variations in, the eflibiencies of the two units represented, respectively, b the elements 5-and 7, on the associated .parts, upon the other hand. If the condensing capacity of the latter unit is greater than the delivery ca acity of the units 5 and 7, additional air will be the breather hole .to compensate for the ethe elements 27 and 22 and drawn throu h ficiency, 'while, if the reverse is the the sur lus expanded gas would be discharge throug said opening 25 To provide for access to the interior of the condenser 22, while, at the same time, providing the maximum degree of insulation against heat losses, I provide the interior casing with aremovable cover 22", and the outer casing with a removable covering 22, the space between the two constituting a vacuum jacket 22, and said space receiving any suitable number of sheets ofemetal foil indicated at 22. The inner and outer casings may be held in. properly spaced relation to eachother by spacing balls 22, of a'material such as porcelain, having a lowdegree of heat conductivity, while, at the same time, possessing the requisite strength for the pur ose According to the Millar and ullivan technical paper 424, issued by the Bureau of Mines, the entropy of nitrogen, the chief constituent of air, is the same at 60 atmospheres and 271 K. as at one atmosphere at From the data furnished by Millar and Sullivan on the total heats of nitrogren vapor and the formula for isothermal compressionof gases, it'is easy to calculate the theoretical work required for this removal of the superheat in the manufacture of liquid air,

which would be the works of isothermal compressures is proportional to the volume of the pression less the work of adiabatic expansion, which per pound of nitrogen would be 108,700 foot pounds and 63,900 foot pounds, respectively, leaving a net expenditure of only 44,800 foot pounds.

The air that is delivered through pipe 20, and which has had its superheat removed, is

brought into heat exchanging relation with the coils connecting the expansion stages of the several turbines, wherein a gas, viz: the hydrogen having a low critical temperature, is, being expanded and contacting with the numerous convolutions of the pipe coils it condenses to liquid form, its latent heat being given up to maintain isothermal expan- Due to the low critical temperature of the expanding gas medium, no condensation of the medium can occur, thus, rendering nearly perfect the transformation of heat into work. Since the work of isothermal compression or expansion between two given gas, and, consequently, to the absolute temperature and the heat given up or absorbed being equal to the mechanical equivalent of the work done, and thenet work expended being equal to the difference between isothermal compression and isothermal expansion, the following formula would apply:

Ht Ht t-t' T T T In this formula, W is the net work expended; H the' mechanical' equivalent of the heat absorbed; t the temperature of isothermal compression, and t the temperature of isothermal expansion. The heat capacity of the gas sion. engines within the' condenser will'notv operate to materially increase its heat 'capacity over the heat capacity of the expandlar and Sullivan on the thermal properties of nitrogen to this formula, I obtain 17 7,460 foot pounds as the theoretical net work of removingthe latent heat of 1 pound of nitrogen vapor. This, added to the network of,

removing the superheat gives'222,260 foot pounds as the minimum theoretical net workof liquefying one poufid of nitrogen vapor.

With good heat insulation and eflicient compressors and expanders, the actual expenditure of energy should not exceed 300,000 foot pounds per poun which would ed gas. Applying the data furnished by Milmean an output of 4.9 liter .per kilowatthour against .95 liters which at present is considered good.

While the apparatus-herein shown and described represents one embodiment which may be utilized in carrying out my ideas, it is to be understood that the invention is not limited to this apparatus, nor to any spe- 'cific type of apparatus, sincemany ways of accomplishing the. same result will readily suggest themselves to those skilled in the refrigerating art. Consequently, it is to be understood that the invention includes within its purview'whatever changes fairly come within either the terms or the spirit of the appended claims.

Having described Ifiy invention, what I claim is 1. The herein described process ofabsorb- I ing and removing the latent heat of condensation of gases having a low condenslng temperature, which consists in compressln a gas having a critical temperature lower t an condensing temperature of the gas sought to be liquefied, expanding said gas substantially isothermally against an external resistance while in heat exchanging're'lation to the sat-- urated' vapor, and returning the expanded as in counter-current with'the said gas to its source of compression.

of gases comprising compressing the. gas'to a pressure where its entropy at a convenient temperature is equal to or less than its entropy' of saturation and expanding substantially adiabatically against an'externalresistance. i

4. The herein described process of remov ing the total heat of a gas above the heat of 3. The process of removing the superheat the liquid, which consists in compressing and expanding the said gas-from a convenient temperature against a suitable external resistance for the purpose of partially or completly removin thesuperheat of the gas, and subsequent y bringing the gas thus cooled in heat exchanging'relation with a precooled gas medium which is expanded against an external resistance and has a critical temperature lower than the condensing temperature pf the said gas for the purpose of absorbin the remaining total heat content above the heat of the liquid.

5.- The herein described'process of removing the superheat of gases, having a very low condensing temperature, which nonsists in compressing the gas and expanding the same substantially adiabatically from a conveniqent temperature against an external resistance preparatory to'the removal of its latent heat of condensation, by other refrigerating means.

6. The adiabaticexpansion of compressed air against external resistance, for the removal of its superheat and the subsequent removal of its latent heat of condensation at constant temperature by refrigerating means.

7. Apparatus of the character described,

' comprislng a gas compressin and expanding means, a condenser to which t e expanded gas is delivered, a second gas compressing means, .a second gas expanding means within the condenser, a conduit through which the gas from the second gascom re's'sing means is delivered to the gas expan ing means within the con denser, and means for conducting the expanded gas from the last named gas expanding means counter-current along said conduit, and back to the second gas compressing means.

8. A structure as recited in claim 7 wherein the second gas expanding means within the -condensor is of multi le stage.

9. Apparatus of t e character described,

co'mprismg'a compressor for gas to be liquefid, an ex ander to which the gas is delivered from sai compressor, and a condenser to which the gas is delivered, said condenser comprising a plurality. of expansion engines.

having a common shaft. 1

I apparatus, means for delivermg thegas compressed thereby to and conducting said gas in series through the several stages of expaning the gas that is travelin to said engines to the action of the gas that 1s being returned from said engines, in heat exchanging relation between the two. 3

13. Apparatus of the character described, comprising a compressor for gas to be liquefied, an expansion engine to which said gas is delivered, a condenser to which the gas 1s delivered fromthe expansion engine, said condenser comprisin a plurality of expansion engines connecte in series by refrigerating coils to the action of which the gas from the first named expansion engine is subjected, a compressor for a gas having a criticaltemperature lower than the condensin temperature of the gas that is being lique ed, means for conductlng the last named gas to the expansion engines of the condenser, and means for returning the gas from said expansion engines to the second com ressor in countercurrent to the flow of gas rom said compres sor to. the said plurality of expansion engines.

14. In the quantity production of liquefied gases, the herein described process of absorbing and removing the latent heat of condensation of gases having a low condensing temperature, which consists in compressing a gas having a critical temperature lower than. the condensing temperature of the gas sought to be liquefied, expanding the said gas while in heat exchanging relation ,with the saturated vapor, and returning the expanded gas in counter-current with the compressed gas to its source of compression.

In testimony whereof I aflix my signature.

LEON B. STRONG. 

